Say what?? A grassy looking cover for a pergola?? I'm thoroughly confused. A pergola is essentially an arbor with a flat (rather than curved), OPEN, top. Where is the grassy looking stuff supposed to go??

he wants it to cover the top for some reason. he wants it to look some what like thatch. he already got an estimate for it and it was around 10,000 bucks so i figured it was worth checking into cause i dont see how it could cost that much

I'm still confused.....does he want a dry roof ("like thatch") or does he want something that's green and growing?

If dry - Google "thatch". If green and growing, that's a whole other ball game because of liner fabrics, bracing for additional weight loads of soil and plant material, etc.. If he requires green and growing, look into pond liner. Then 3" of good topsoil. then creeping thyme: it smells good, looks good, and flowers.